1. Field of the Invention
The present invention relates to a rigid-flexible substrate and a method for manufacturing the same.
2. Description of the Related Art
In recent years, so-called printed substrates having a conductor wire layer formed on a surface of a thermoplastic resin sheet have been applied to packages incorporating circuit boards and semiconductor elements, and the like. In addition, as more layers of wires are laminated, conductor wire layers between different layers are electrically connected by a via conductor.
Further, rigid-flexible substrates formed by integrating a flexible printed substrate (flexible portion) and a rigid substrate (rigid portion) have been known. The rigid-flexible substrate generally has advantages in that it is excellent in component mounting properties because its rigid portion has rigidity equal to that of the rigid substrate, and that it can be incorporated into electronic equipment in a three dimensional manner and can also be applied to a hinge portion (bent portion) and the like because it has flexibility similar to that of the flexible substrate as a whole. Furthermore, the flexible substrate alone is very thin and difficult to handle, and thus requires a dedicated mounting facility, whereas the rigid-flexible substrate, whose rigid portion has high rigidity, also has advantages that an existing mounting facility for rigid substrates can be used and mounting density can also be increased.
Examples of a method for increasing hardness of a rigid portion include a method of using a hard material such as glass epoxy as a substrate material for a rigid portion, a method of setting a rigid portion to have a wire density higher than that of a flexible portion or to have more layers than those of a flexible portion in a substrate, and the like. Japanese Patent Laid-Open No. 2002-305382 discloses a rigid-flexible substrate fabricated by laminating thermoplastic resin sheets 3 having conductor wires (not shown) and via conductors 4 formed therein such that a rigid portion and a flexible portion have different numbers of laminated layers, and performing collective multilayer pressing on thermoplastic resin sheets 3 (FIG. 5). In this case, there has been a problem in that a crack, peel-off, or the like is likely to occur at a junction between the rigid portion and the flexible portion.
On the other hand, Japanese Patent Laid-Open No. 2004-319962 discloses a flex-rigid printed wiring board (rigid-flexible substrate) configured to connect a plurality of rigid substrates (such as FR-4 as glass epoxy substrates) having a wiring pattern, using a flexible portion composed of a resin sheet having insulation properties and flexibility. Japanese Patent Laid-Open No. 2004-319962 discloses that, by forming a chamfer at an end portion of such a rigid substrate (i.e., on a side connected to the flexible portion), repeated bending strength does not vary depending on the position, and a peel-off at a junction between a rigid portion and the flexible portion can be suppressed.
However, the method described in Japanese Patent Laid-Open No. 2004-319962 is a method of chamfering a printed wiring board having a certain degree of hardness (i.e., the rigid substrate such as a glass epoxy substrate) by machining with a router. Accordingly, the flex-rigid printed wiring board described in Japanese Patent Laid-Open No. 2004-319962 is basically different from the rigid-flexible substrate having a rigid portion and a flexible portion formed to have different numbers of laminated layers as described in Japanese Patent Laid-Open No. 2002-305382. Further, in the method described in Japanese Patent Laid-Open No. 2004-319962, the printed wiring board is required to have hardness, and it is difficult to accurately polish a rigid-flexible substrate formed by laminating soft resin sheets. Furthermore, when a component is downsized, it is difficult to accurately polish the component by machining with a router, and manufacturing cost is also increased.